Severe asthma represents ~10% of all asthma but carries a significantly greater mortality risk especially for African descent (AD) individuals. Environmental factors (such as exposure to particulate matter air pollution or PM) and genetic factors are likely critical to defining susceptibility to severe asthma and provide insights into tis area of serious health disparity. In this regard, the non-muscle isoform of myosin light chain kinase (nmMLCK), encoded by MYLK, actively participates in the pathogenesis of vascular barrier disruption and lung inflammatory cell trafficking, each an essential contributor to asthmatic inflammation. In lung endothelial cells (EC), nmMLCK is a multifunctional cytoskeletal mediator central to regulation of EC actin cytoskeletal rearrangement via phosphorylation of myosin light chains (MLCs). Our previous studies further identified that African ancestry is associated with asthma risk with coding and non- coding single nucleotide polymorphisms (SNPs) in the gene encoding nmMLCK, MYLK, over-represented in AD individuals strongly associated with severe asthma. This R01 renewal will characterize the pathobiological functions of MYLK SNPs associated with severe asthma in under-represented minority backgrounds, thereby directly addressing an important health disparity. To address our hypothesis that nmMLCK expression and functional activity (inflammatory regulation) are dysregulated in severe asthma & influenced by SNPs enriched in AD populations, Specific Aim #1 will evaluate MYLK SNPs found in non-hispanic caucasians, Latino & African descent children and adult populations for association with severe asthma. We will conduct mid-throughput genotyping studies in ~4000 asthma patients (European descent, African descent, Latino Puerto Rican, and Latino Mexican)and identify severe asthma-related SNPs. Specific Aim #2 will characterize the effects of severe asthma-associated SNPs and Paticulate Matter (PM) exposure on nmMLCK mRNA expression and function via effects on MYLK 5'UTR promoter activity, 3'UTR binding activity to miRNAs, promoter CpG island methylation, and mRNA secondary structure. Specific Aim #3 will functionally analyze effects of severe asthma-associated MYLK coding SNPs on nmMLCK protein structure and function (kinase activity, protein binding, and lamellipodial dynamics). Finally, Specific Aim #4 will validate these severe asthma-associated SNPs in vivo, and evaluate novel nmMLCK inhibitors designed to diminish PM-exacerbated asthmatic inflammatory lung injury. Supported by compelling published and preliminary data, we believe these integrated translational studies will lead to mechanistic insights into asthma pathobiology and the health disparity of severe asthma while facilitating the development of novel, potentially population-specific, inflammation-reducing therapies for asthma.